Final fix as suggested.
Final fix as suggested.

This fixes the hanging bug, and can server the large file multiple
times. It's also pretty fast.

python-hyper/hyper-h2,Kriechi/hyper-h2,vladmunteanu/hyper-h2,vladmunteanu/hyper-h2,bhavishyagopesh/hyper-h2,Kriechi/hyper-h2,python-hyper/hyper-h2